Truck drivers have requested the National Labor Relations Board (NLRB) look into a series of complaints from drivers claiming they were victims of workplace retaliation from employers.

The drivers assert their employers have used retaliatory tactics in response to their efforts to collectively bargain and improve their working conditions. The drivers cited examples of retaliatory measures from employers, which include withholding jobs and intentional “dispatch delays” that force truckers to wait for hours for their loads.

The NLRB has recently taken action in favor of truckers, including in February, when an NLRB judge ordered a trucking company to reinstate six drivers. The judge also ordered the company to compensate the six drivers, who were were fired the day after voting to unionize in 2015.